ECOLOGICAL BACKGROUND AND GROWTH BEFORE 1900 



25 



According to Adams, any of these responses 

 might properly be considered ecological. 



rhe treatment of developmental, tolera- 

 tion, and response physiology may be tested 

 by the first of these queries. The present 

 section is written about the second; the 

 third point will be considered later. At the 

 turn of the century, the present discussion 

 would have centered about the history of 

 the ecology of species as distinct from that 

 of individuals. Now, in the 1940's, it is con- 

 cerned with populations. The difference is 

 not great, since current definitions of a 

 species are in terms of natural populations 

 or groups of populations. 



The study of populations is not so far 

 removed from developmental, toleration, 

 and response physiology as at first appears. 

 Even the mathematical theory of popula- 

 tions is built around a framework of facts 

 or assumptions concerning animal behavior 

 (cf. Thompson, 1939). The primary biolog- 

 ical functions of a population include the 

 birth, nutrition, growth, reproduction, and 

 death of its members. As organisms or 

 populations grow, they draw their food 

 from outside themselves and may efiEectively 

 diminish the surrounding food supply. 



Malthus (1798), an early student of 

 populations, calculated that while numbers 

 of organisms may increase in geometrical 

 progression, their food supply may never 

 increase faster than shown by an arithmet- 

 ical progression; a resulting discrepancy fre- 

 quently develops between the population to 

 be fed and the available food. Malthus 

 identified the drive for coitus with that for 

 reproduction, and at first thought both were 

 inexorable in man, as in other organisms. 

 As a result, there arises, he said, a violent 

 competition, which leads to a struggle for 

 existence (his phrase) until population in- 

 crease is finally controlled by catastrophe 

 or, in man (1803 edition), by purposive re- 

 straint from procreation. 



As ecologists, we may happily avoid the 

 bitter controversy that sprang up almost 

 immediately about the matter of human 

 birth control and focus our attention on 

 the more general imphcations of the Essay 

 on Population. The ideas were not entirely 

 new, and much of the earUer history can 

 be found in the discussion of pre-Malthus- 

 ian doctrines of population by Stangeland 

 (1904). Machiavelfi, 275 years before 

 Malthus, had realized the danger that hu- 



man populations may increase beyond the 

 means of subsistence in Umited areas and 

 that such an increase would then be 

 checked by want and disease. Botero pre- 

 sented a similar thesis in 1590. Hale 

 (1677), Buffon (1751), Franklin (1751), 

 Wallace (1761), and Bruckner (1767), 

 among others, anticipated Malthus. In fact. 

 Hale stated that the increase in human 

 population tends to occur in geometrical 

 ratio, which is one of the important proposi- 

 tions of Malthus. Yet it was Malthus who 

 focussed attention on the problem and so 

 set the stage for all demographic studies in 

 sociology and for the controversy about the 

 "struggle for existence" in biology. 



Darwin (1859) found one of the bases 

 for his theory of natural selection in the 

 reasoning of Malthus, and A. R. Wallace 

 was also influenced by it when independ- 

 ently arriving at nearly the same evolu- 

 tionary ideas (Darwin and Wallace, 1858). 

 Twenty-four years before the pubhcation of 

 the Origin of Species, Quetelet, the Belgian 

 statistician, assumed (1835) that resistance 

 to the growth of a population increases in 

 proportion to the square of the rate of 

 population growth, much as the resistance 

 to a projectile increases with the square of 

 its speed. Quetelet speaks of a population 

 as though it were an entity. 



Verhulst, a student and a colleague of 

 Quetelet's, in 1838 published a short essay 

 entitled "Notice sur la loi que la population 

 suit dans son accroissement," in which he 

 cited the ideas of "le celebre Malthus" and 

 those of Quetelet and proceeded to develop 

 briefly an equation describing the course of 

 population increases in proportion to popu- 

 lation density. His equation plotted into the 

 now well-known S-shaped population curve 

 with upper and lower asymptotes, which he 

 called the logistic curve. In his original 

 paper, Verhulst gave certain tests of good- 

 ness of fit of this curve against data for a 

 few human populations of western Europe. 

 Verhulst died in 1849 at the age of forty- 

 five. His work on populations attracted little 

 attention. Miner (1933) found only one 

 reference to it in "modem times" before the 

 rediscovery of the logistic curve by Pearl 

 and Reed in 1920; thus population studies 

 were long dominated by the cruder and 

 partially erroneous ideas of Malthus. 



There seems to have been a general inter- 

 est in human populations in the early dec- 



